Tsunami on Koh Samui?

In June I discussed the possibility of earthquakes in Koh Samui. This month I will look at the possibility of a tsunami affecting the island.
Since the catastrophic tsunami of 2004 which caused so much destruction around the Indian Ocean there have been many studies published on tsunamis, their generation and consequences. There has been nothing specific to Koh Samui that I could find but there are numerous studies relating the possibility of a tsunami in the Gulf of Thailand.

There are three principal causes cited for the promulgation of a tsunami, sub-sea earthquakes, landslides and volcanic eruptions – the former being the most common. Earthquakes are the consequence of the movement of the tectonic plates moving against each other and similar movements in the fault lines which cross them. Major earthquakes commonly occur along the plate boundaries and in SE Asia the ones we are concerned with are the Sunda Trench to the west of Thailand and the Manila/Luzon Trench immediately to the west of the Philippines. Any tsunami generated by an earthquake in the Sunda Trench will not affect Koh Samui due to the land mass in between. All studies I have found re the Gulf of Thailand concern themselves with the effects of earthquakes in the Manila/Luzon Trench.

“PROBABILISTIC TSUNAMI HAZARD ANALYSIS AND RISK TO COASTAL POPULATIONS IN THAILAND”
Follow the link for the full report but to summarize a seismic induced tsunami in the southern part of the Manila Trench in excess of 8.5Mw would likely lead to a tsunami entering the Gulf of Thailand once
in 650 years to a height of 2-3 metres. The worst affected areas would be the southern provinces.


This is demonstrated in the “2010Tsunami Simulations for Regional Sources in the South China and Adjoining Seas” study which proposed a catastrophic earthquake at the Luzon Trench, off the western shore of Luzon producing a tsunami affecting the Narathiwat and Pattani provinces in Thailand. It also addresses the effects of a sub-sea landslide off Borneo but generally the shallow nature (average 100m) would mitigate the magnitude of any tsunami entering the Gulf of Thailand and hence the affect on Koh Samui.
The study “Effect of Tsunamis generated in the Manila Trench on the Gulf of Thailand 2008” states “The Gulf of Thailand is affected by the diffraction of tsunamis around the southern part of Vietnam and Cambodia. The tsunami amplitude at the southernmost coastline is about 0.65 m for the Mw 9.0 earthquake. The current velocity in the Gulf of Thailand due to the Mw 9.0 earthquake is generally less than 0.2 m/s. “
“Tsunami Risk Reduction Measures Phase 2 –November 2009” stated “The simulations reveal further that tsunami threat due to seismic origin to the Gulf of Thailand is almost nonexistent.”

The conclusion is that , yes, Koh Samui could be affected by a tsunami, but that it would be small and not very powerful, probably less than one metre.